1. Field of the Invention
This invention relates to a rotary sensor and more particularly to a rotary sensor capable of detecting with high precision a rotation angle transmitted from outside.
2. Description of Related Art
A conventional rotary sensor has an unillustrated housing of an approximately cylindrical external shape, in which a disk-like rotator 1 is housed as shown in FIG. 10. The rotator 1 has a bearing portion 1b which projects to the right in the drawing from the center of a disk-shaped flange 1a. At the center of rotation of the bearing portion 1b, an oval-shaped shaft hole 1c is formed to a specific depth. In a part of the flange 1a near the root of the bearing portion 1b, a spring retaining portion 1d is projectively formed.
Around the bearing portion 1b a torsion coil spring 2 is mounted to elastically force the rotator 1 in a direction of rotation. The torsion coil spring 2 is retained at one end by the spring retaining portion 1d and at the other end on the housing side not shown.
On the left side surface of the flange 1a of the rotator 1 a slider piece not depicted is attached. On the opposite side of this slider piece an unillustrated resistor board on which a resistor pattern is formed is disposed. When the slider piece slides in elastic contact with the resistor pattern with the rotation of the rotator, the resistance value varies, thereby enabling detection of rotation angle of the rotator.
The conventional rotary sensor in use as an unillustrated throttle valve rotation sensor on an automobile will be explained. The throttle valve is coupled with the drive shaft 3 which transmits rotation of the throttle valve. The forward end 3a of drive shaft 3 is formed oval in configuration. When the conventional rotary sensor is attached on the throttle valve side and the drive shaft 3 is inserted into the shaft hole 1c of the rotator 1, the rotation of the drive shaft 3 is transmitted to the rotator 1.
The drive shaft 3 stated above is somewhat loose, and relatively off-centered, in a radial direction orthogonal to the axial direction because of assembly requirements of components on the throttle valve side. Absorption of this looseness or deviation from center of the drive shaft 3 has been required on the rotary sensor side.
In the conventional rotary sensor, therefore, the oval shaft hole 1c is made slightly larger in width and diameter than the forward end portion 3a of the drive shaft 3, so that the drive shaft 3 may be loose-fit in the shaft hole 1c to absorb the radial looseness and relative deviation from center of the drive shaft 3.
Since the drive shaft 3 is loose-fit in the shaft hole 1c, there occurs a backlash with the rotator 1 when the rotator 1 is rotated by the driven shaft 3, causing an error in the rotation of the rotator 1, resulting in a failure in proper detection of rotation angle on the drive shaft 3 side. To obviate this drawback, the torsion coil spring 2 is adopted to constantly apply an elastic force to the rotator 1 in one direction towards rotation in relation to the drive shaft 3, thus absorbing the backlash.
That is, when the drive shaft 3 rotates in one direction, the rotator 1 rotates in one direction against the spring force of the torsion coil spring 2. When the drive shaft 3 rotates in the other direction, the rotator 1 is independently rotated in the same direction with the spring force of the torsion coil spring 2.
The rotation angle of the drive shaft 3, therefore, cannot be detected with high precision if the drive shaft 3 has radical looseness in a radical direction and relative deviation from center.
The conventional rotary sensor stated above, however, has such a problem that the torsion coil spring 2 used therein is expensive because of a special configuration and accordingly the high cost of the rotary sensor results.
Since the drive shaft 3 is loose-fit in the shaft hole 1c, there will take place friction between the drive shaft 3 and the shaft hole 1c during a long-time use, resulting in difficult high-precision detection of rotation angle.
In view of the above-described problems of the heretofore known rotary sensor, it is an object of this invention to provide a rotary sensor which ensures high-precision detection of rotation angle by absorbing looseness and relative deviation, if any, from center of the drive shaft 3 with respect to the rotary sensor.
As the first arrangement for solving to the above-described problems, the rotary sensor of this invention is comprised of a drive shaft having a flat portion at the forward end portion, a rotator provided with an engagement hole having a flat portion in which the forward end portion of the drive shaft is inserted, an elastic member having an elastic contact portion, and a rotation angle sensing member for detecting the rotation angle of the rotator; the rotator having a groove formed in parallel with the flat portion adjacently to the flat portion of the engagement hole, and a partition wall between the groove and the flat portion of the engagement hole; the partition wall having an open portion, through which the engagement hole communicates with the groove, from the opening to a specific depth of the engagement hole; and the elastic contact portion of the elastic member inserted in the groove projecting to the engagement hole side through the open portion, into elastic contact with the flat portion of the drive shaft.
As the second arrangement for solving to the above-described problems, the elastic member is made of a plate spring and the elastic contact portion is projectively formed with the plate spring partly curved. The crest of this curved part is projected to the engagement hole side into elastic contact with the flat portion of the drive shaft.
Furthermore, as the third arrangement for solving to the above-described problems, the elastic member has a retaining portion formed by raising on the opposite direction of projection of the elastic contact portion, to thereby retain the elastic member.
Furthermore, as the fourth arrangement for solving to the above-described problems, a through hole is formed in the curved crest part of the elastic contact portion.